1. Field of the Invention
The present invention relates to the detection of vibration in an electric powered vehicle and more specifically to the detection of vibration in an electric powered vehicle having traction motors powered from a source of switched DC power.
2. Description of the Prior Art
Mass transit vehicles are often utilized to transport passengers along fixed routes. High voltage DC electric power is often provided to such vehicles via an electric line or an energized rail that traverses the fixed path. Electrical energy from the electric line or the third rail is brought into the vehicle via a pantograph or a brush assembly.
Such vehicles often include AC traction motors for imparting motive force to the wheels of the vehicle. One or more inverters are positioned between the incoming high voltage DC and the AC traction motors. The inverters transform the high voltage DC power into a switched DC power. The switched DC power synthesizes a three-phase sinusoidal waveform which is fed to the AC traction motors. The AC traction motors convert the switched DC power into rotational motion that is utilized to impart motive force to wheels of the vehicle.
A typical inverter includes six power switching devices that are controllably switched ON/OFF to synthesize the three-phase waveform supplied to the AC motors. If all six power switching devices are operating properly, motive power is delivered uniformly to the wheels. In response to the uniform delivery of power to the wheels, passengers transported in the vehicles experience relatively smooth acceleration and operation. If, however, one of the six power switching devices is not switching properly the output of the inverter is not a three-phase sinusoidal waveform.
In the absence of receiving a three-phase sinusoidal waveform, the AC traction motor delivers power non-uniformly to the wheels of the vehicle. This non-uniform delivery of power is detected as vibration in the vehicle. This vibration is more pronounced during acceleration of the vehicle and at speeds less than 30 miles per hour. Above 30 miles per hour the rotational inertia of the motor and the linear inertia of the vehicle tend to dampen the vibrations caused in the absence of one of the power switching devices not operating.
It is an object of the present invention to provide a method and apparatus for the detection of the presence of vibration in a vehicle caused by the non-operation of one of the power switching devices in the inverter. It is a further object of the present invention to take suitable corrective action to reduce or eliminate the vibration caused by the non-operation of one of the power switching devices.